[Patent literature 1] JP 2011-186589 A
A control system is known which uses a control target model to perform non-interference control so as to negate or eliminate mutual interference caused by a plurality of control quantities outputted by a control target (refer to Patent literature 1). Such non-interference control negates the mutual interference by previously adding a quantity equivalent to the mutual interference to the control quantity.
Generally, a control target model, an input signal, or an output signal may suffer unintentional disturbance. Therefore, when a control target has a great number of control quantities of inputs and outputs, to pose a great number of combinations of mutual interference, it becomes difficult to realize non-interference control in calculating a transfer function etc.
Examples of control systems that pose mutual interference include a vehicle steering control system, which operates a plurality of steering actuators depending on steering wheel manipulation by a driver on a vehicle to thereby control actual steering angles of front wheels and rear wheels. To be specific, the actuators include an electric power steering which assists a steering torque of a steering wheel by a driver; a variable gear transfer steering which flexibly changes a turning angle of a front wheel with respect to a turning angle of the steering wheel; and an active rear steering wheel which flexibly changes a turning angle of a rear wheel with respect to a turning angle of the steering wheel.
Operations of the plurality of actuators output several vehicle motion properties such as a steering angle θs, a yaw angle velocity γ, and a lateral acceleration ay. At this time, the plurality of actuators operate cooperatively with a rotational movement axis (yaw axis) around the center gravity of the vehicle, involving mutual interference. Furthermore, the vehicle receives disturbance due to rainstorm, blown fragments, or a road surface reactive force depending on the grounding state between tires and road surfaces. Such disturbance cannot be detected or presumed in real time practically by any measure.
Thus, it is not realistic to achieve non-interference control, which presumes mutual interference between the vehicle motion properties based on operations of a plurality of actuators and which adds previously a quantity equivalent to the mutual interference to a control quantity. To that end, a person with a skilled technique needs to make trial-and-error to adjust each of the actuators; this requires a number of time and man hours. The above situation may arise not only in a vehicle steering control system but also in a control system that may undergo mutual interference between a plurality of outputs of a control target.